I bought this mute because I cannot play the sax at my house due to some building ruleS (Swiss rules, yay!). This clearly reduces the sound to a normal TV (more or less 20 of volume) and the sax cannot be heard from outside my appartment.
Given that the sound is reduced to a normal TV volume, I cannot play it during the night, it's just too much sound.
Regarding how to assemble it, it's quite easy and adjustable, I consider it usable for market's standard saxophones. Totally fine for a JAS-769.
A give my best point to the sound when you plug your headphones to the microphone, it's really awesome and more when you put some audio in and some echo directly.
My worst point goes to the difficulty to play the high notes of the left hand and altissimo ones. Due to the neoprene pads, it's quite difficult to move and adjust the hands quickly. Regarding the low notes, I don't have any problems, I only need to concentrate more when going below C, but it's also possible (a bit disturbing for studies of 8a jumps)
I completely recommend the mute, it saved my sax player life here in Switzerland. Without it, I would have almost never played again :)